The one-electron oxidation of hydroxy(tetramesitylporphyrinato)iron(III)

Abstract

The oxidation of hydroxy(tetramesitylporphyrinato)Fe(III) ([Fe(tmp)]OH) has been investigated by voltammetric and spectroelectrochemical techniques in CH2Cl2 containing tetra(n-butyl)ammonium hexafluorophosphate as supporting electrolyte. In this medium, the first one-electron oxidation is reversible on the time scale of cyclic voltammetry. The UV–vis spectrum, as obtained by double potential step chronoabsorptometry, indicates that the oxidation is centered at the porphyrin ring to form the corresponding π-cation radical. At longer times, or higher potentials, oxidation of [Fe(tmp)]OH leads to loss of hydroxide and formation of [Fe(tmp+)]PF6 π-cation radical. The time-dependent process is consistent with an ECE type mechanism, with the chemical step being slow conversion to neutral [Fe(tmp)]PF6. At higher potentials, the initial oxidation product loses a second electron. The overpotential dependent oxidation suggests an EEC type mechanism with the second electrochemical step being a slow heterogeneous electron transfer from the Fe-OH moiety.Key words: hydroxy(tetramesitylporphyrinato)iron(III), oxidation, electrochemistry, spectroelectrochemistry, π-cation radical.